Recognize RISCV_WITH_RVV env var on RISC-V to set WITH_RVV cmake var

Cargo-zng.toml

@@ -38,5 +38,15 @@ libc = "0.2.43"
 [build-dependencies]
 cmake = "0.1.50"
 
+[features]
+# Experimental: This feature only affects zlib-ng, is only relevant to riscv64
+# targets, and currently only has an effect when `cmake` is used. It builds
+# binaries portable to machines without RVV, even if the build machine is
+# riscv64 and detected to support RVV. This is useful for building a more
+# portable binary, or on systems where auto-detection is incorrect (as in
+# https://github.com/zlib-ng/zlib-ng/issues/1705). Building with the `RVV_OFF`
+# environment variable set (to any value) is equivalent to this feature.
+rvv-off = []
+
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(zng)'] }

Cargo.toml

@@ -89,6 +89,14 @@ zlib-ng = ["libc", "cmake"]
 # or be completely removed in the future
 zlib-ng-no-cmake-experimental-community-maintained = ["libc"]
 stock-zlib = []
+# Experimental: This feature only affects zlib-ng, is only relevant to riscv64
+# targets, and currently only has an effect when `cmake` is used. It builds
+# binaries portable to machines without RVV, even if the build machine is
+# riscv64 and detected to support RVV. This is useful for building a more
+# portable binary, or on systems where auto-detection is incorrect (as in
+# https://github.com/zlib-ng/zlib-ng/issues/1705). Building with the `RVV_OFF`
+# environment variable set (to any value) is equivalent to this feature.
+rvv-off = []
 # Deprecated: the assembly routines are outdated, and either reduce performance
 # or cause segfaults.
 asm = []

zng/cmake.rs

@@ -14,6 +14,9 @@ pub fn build_zlib_ng(target: &str, compat: bool) {
             .define("WITH_DFLTCC_INFLATE", "1")
             .cflag("-DDFLTCC_LEVEL_MASK=0x7e");
     }
+    if target.contains("riscv64") && (cfg!(feature = "rvv-off") || env::var_os("RVV_OFF").is_some()) {
+        cmake.define("WITH_RVV", "OFF");
+    }
     if target == "i686-pc-windows-msvc" {
         cmake.define("CMAKE_GENERATOR_PLATFORM", "Win32");
     }